Signaling system



April l, 1947. E. R. TAYLOR 2,418,145

i SIGNALING SYSTEM Filed Feb. s, 1943 5 sheets-sheet 1 A T TORNEV n L 4 n k kwuhs 5 Sheets-Sheet 2 April 1, 1947. R. TAYLOR SIGNALING SYSTEM lFiled Feb. 5, 1945 /NVENTOR BV E. TAYLOR AHORA/EP .mlm

April l, 1947.

E. R. TAYLOR SIGNALING SYSTEM Filed Feb. 3, 1943 5 Sheets-Sheet 3 ATTORNEY April l, 1947. E. R. TAYLoR SIGNALING SYSTEM 5 Sheets-Sheet 4` Filed Feb. 5, 1945 Fff FH@ "//V NTOR E. MVLOR 4 P ATTORNEY of the receiver. van electrical timing device which may be suitably adjustedto cause the limiter to beheld at Patented Apr. l, 1947 SIGNALING SYSTEM Edmund R. Taylor, Pelham Manor, N. Y., Aassignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 3, 1943, Serial No. 474,531

Claims. 1

.Thisinvention relates tosienaling systems and more particularly to a signaling system in which ,means Aare provided for transmitting and receiving, over a suitable transmitting medium, altermating current pulses composed cfa combination ,quency range.

.The main object of the invention is the pro- -v-isiomin -a receiving circuit adapted Yto receive and amplify alternating current impulses .corn-` posed of a combination of frequencies lying within `a comparatively narrow signaling band, of means for reducing the Yquantity of .amplied energy at the beginning of each pulse below a predetermined value, and to increase this energy automatically after a `predetermined interval to .the .desired level for ,operating the responsive devicesiof the receiver.

wlin alternating current receivers, particularly those employing volume .limiters to control the energy applied to the responsive .devices vof the receiver, it has .been found ,that where the pulses are generated at the transmitting end of the line `by keying devices, the `chatter .of .the contacts 4often causes the production `of transients which are abnormally large. Ordinarily the ceiling .of the volume limiter is xed at a value suiciently high for the receiver to accept pulses coming over the line with rather large loss frequency distortion. The intensity of the transient currents produced by contact chatter, on the other hand, is so high that. although the frequencies composing the disturbance are similarly attenuated during their transmission, the value of Isome frequency therein, even if leveled off by Vthe ceiling of the limiter at its established value,

fheld below the level at which transient disturbanes produced `by contact chatter and amplied to said level lcan cause any false operation The network is provided with *the protective low level for the duration of the transient disturbance which forms the advance portion of the pulse, subsequent to which the amplication of the limiter is then automatically Vraisedto the level appropriate to the passage of f the remainder of thepulse.

Another object oi tbe invention which is acof frequencies preferably within the voice fre- Y screen grid tubes, of the amplification factorof the tubes so that maximum effectiveness Ais obtained from their operation `at the initial .protective low level ci ampliiication and at the ultimate high level of ampliication. .It is well known, Vfor example, that for the maximum .effectiveness .at any `level of Yampliiication there is `an optimum relationship between `the plate voltage Aand the screen 4potential of a screen ,grid tube, and that .if .the level oramplicationis changedfand maximum effectiveness .is desired at the new level, the plate and screen voltages must be readjusted with respect to each other to the values indicated kfor'that level. By means of my invention, the network which controls the lowering and the raising of the limiter ceiling, which it accomplishes bylowering` and raising, respectively, the available potential across the cathode-anode electrodes of the limiter tubes, automatically and simultaneously readiusts the screen potentials to values precalculated to be those required for theparticular potential differences then appliedL across the cathodes .and anodes of the tubes.

These and other objects of the invention will be more readily ascertained from the following description and appended claims, taken in convnecti-on with the following drawings, in which:

Fig. l Ishows the transmitting station Aa. `trunk selecting apparatus by Vmeans of which `the receiving circuit of the invention may be connected to the trunk and to the transmitting station; and a skeletonized showing of two telephone connections which may 'be established` byfsettable apparatus responsive to the operation of the receiver;

Fig. 2 shows the amplifier and detector circuit of the receiver incorporating `the network of Ymy invention;

Fig. Sshows the check circuit for checking the accuracy of the received impulses and the circuit which responds to the conditioning or KP impulse;

Fig. 4 shows a group of conventionalregisters settable in response to the received impulses, and -a conventional showing of a circuit known as a fmarker which is adapted `to operate Yin inclusive, are to be .disposed relative to each other Y in orclcr to disclose the `invention completely.

It will be readily ,understood `by those skilled in the signaling artsthat a signaling system ar- "ftransmitting station,

, ing current impulses is adaptable to a wide variety of uses, especially indicated by the application to be made of the intelligence conveyed by the impulses transmitted over the system. My invention may, of course, be utilized in any alternating current receiver in which it is desired to automatically lower and raise the level of Varnplification forthe purposes mentioned or for any other purpose, and in order to describe the elements of the invention, its operation and its flexibility, I have chosen to disclose it in connection with its adaptation t a telephone system of the kind described in Patent No. 2,232,912, issued to G. Hecht, A. A. Lundstrom, and E. R. Taylor on October 26, 1943, in which a calling subscriber, desiring a connection with a distant station which can only be reached bytrunking facilities avail- "able at an operators position in an office within the dialing area of the calling subscriber, dials the operator who, upon receiving from the calling subscriber the oiiice and line number of the desired station, selects a trunk extending in the desired direction and causes a group of alternating current impulses indicative of the called office and station designations to be transmitted thereover into settable apparatus at the office in [which the trunk terminates, wherefrom this apparatus then controls the selective positioning of a suitable number of switches by means of which [the trunk connection is further extended to the Ldesired station. Itis obvious, however, that while 'this application of the invention will illustrate its purpose, scope and operation, the invention itself is susceptible of other uses readily appreciated by those skilled in the signaling art.

n Referring, now, to the drawings, the subscriber A establishes a connection to the operators position within his dialing area by the well known Y means referred to in said above mentioned patent and, at said position herein referred to as the Y informs the operator thereat that he desires to establish a connection to' subscriber B whose station terminates in oflice Y, which can be reached from the transmitj ting station over a trunk line that interconnects said transmitting station with oiiice X and by .automatic trunking facilities between office X v and oiiice Y which are selectively connectable to ,the trunk therebetween by equipment at oice X which operates in response to the receiving circuit subsequent to the latters response to the impulses transmitted over the trunk from the transmitting station. The operator, upon learning of the desired office and station from the callconnected through the right-hand plug of the cord and jack JA to conductors T and R, respectively, of the trunk thus taken into use.'

The key-set KS at the operators positionv comprises a series of digit keys 0-9,`a key ST and akey KP, and all of said keys are suitably wired to six separate'sources of alternating'current frequencies a, ,f within the voice frequency a range, in a manner such that the depression of each of thekeys will cause two of the frequenciesv to be applied across conductors T and R of the trunk via conductors SCT and SCR in the followiing,` `combinations through circuits completed from the sources of frequencies involved and the '4 undesignated resistances connected to the stationary springs of the keys:

Frequencies At office X, the trunk selected by the operator automatically causes the connection thereto of an idle register sender over suitable selecting equipment, for example, a sender selector device SS comprising a cross bar switch and circuits for the control thereof. Into this register sender is incorporated the receiving circuit to which my invention is applied; that is, the circuit whichreceives the alternating current impulses that will be transmitted by the operator through the manipulation of the key-set KS, and this receiving circuit, upon receiving the impulses, first checks them for accuracy and then causes them to become set up on groups of settable registers connected to the receiver. From the registers, the registration therein is then transferred to a marker circuit and the marker, in response to the transferred registration, then controls the operation of a cross bar trunk selector TS by which the trunk T, R, between the transmitting station and oiiice X, is selectively positioned into connection with another trunk that extends between ofiice X and oice Y, at which latter ofce the sender at oice X then transmits over the trunk to a sender in oice Y pulses that designate the called number, whereupon said sender ,at office Y then initiates operations by which the connection is further extended to the terminals of the called line.

In View of the fact that the sender and marker are well-known equipment elements now extensively utilized in automatic telephony, and vsince the present invention is confined to a signaling system the receiving portion of which is incorporated in such a sender only by way o f disclosing the parts, principles and operation of. the receiving circuit, neither the sender nor the marker is" disclosed except by conventional indications, the disclosure ofthe sender being conflned to the incorporated signal-receiving circuit in its entirety and to a schematic showing of typical settable registers operating in response thereto. s

The receiving circuit to which my invention isV applied by way of illustration, is shown in Figs.

2 and 3, and is essentially a circuit for translating alternating current signal impulses consistingof y various combinations of frequencies sent out from the transmitting station two at a time, into direct current indications suitable for registration in Van associated settable register which comprising a part Yof the sender, operates in response to the registration to complete the call in the usual manner. i Y i The receiver comprises a volume limiter VL; a signal present channel including the highpass 'filter HPF, transformer SPT, a vacuum tube S, a polarized relay SPR and associated circuit; a plurality of receiving. channels, one foreach frequency in the entire signal band a f. f, each of which comprises a band-passilter BPF- va vacuum` tube T-andfapolarized relay R-'such as,- for instance, the channel reserved for 4freouencyia Which is madelup ethanol-pass iilter BPFa, a vacuum tube Ta and a relay Rc.

network-of my invention bywhich the ampiiiication level-.of the limiter VL is automatically raised from its` initially low protective level to its normally high receiving level and by which the .screenpotentials for the tubes Lt andL of the limiter are automatically adjustedfto appropriate values for each case, comprises the `resistances .all vvired` in the interrelated `manner shown in Fig. 2; the key-pulse signal Circuit comprises vrelays KPI KPS and associated circuits which operate in response to the 4initial, operations of'relays Rc and Rf of the channels reserved for frequencies candf, respectively, when `the key KP is operated at the transmitting station` asfhereinaiter set forth; and the check circuits comprise relays CKI 0K3 and associated networks which operate in the manner hereinafter set forth to check the `pulses as they are=received by the various channelsraiectedyby `the frequencies in the impulses.

The alternating current signals, which are al ternating current voltages available across conductorsv T and R of the trunk after the initial transients are dissipatedxare received and appliedto the input elements of the receiving circuit after relay SW iszoperated in any suitable manner. The input elements or the receiving `circuit comprise the adjustable pad AP, which is a means for adjusting `the sensitivity of the .receiving ,circuit tothe minimum required since, `by keeping the sensitivity as low as possible, the likelihood of false .operation on currents which may be produced by speech or noise is materially reduced; the terminating resistance IN,.the cen- .tertap of which` is grounded; 'and .the input transformer IT, the input Winding of vwhich is connected to the terminalsiofresistance IN and the outputvvinding of which is connected tothe common terminal of resistance RG-I` and paralleled condenser CGI, and the common `terminal of resistance RG2 and paralleled condenser CGE. The other common terminal of resistance RG! and condenser CGI is, in turn, connectedto grid G! of Vacuum tube L! while that of resistance -RGZf and condenser CGE Vis connecte-d to grid G2 of vacuum tube L2.

The volume limiter VL comprisesthepentode Avacuum tubes Lt and 'L2 `and their' associated vinput and output circuits. rated in thevvell-knovvn push-pull relation With `the output of their respective anodes connected together by means'of retardation coil L and` delivered, through the blocking condenser-BC and resistance N|,to resistance N5. iter provides adequate ampliiication ofthe incoming alternating current impulses to `cause operation of .thedesired channels but, however, limits its output signal voltage to` such-a value Ythat channels other than: those intendedxto he responsive to the frequencies in the signal will not operate onV the transient currents generated atchannelilter outputs-of filters BPEL?. BPEf by said signals when they start andstop.

The limiting action of the voli-'me limiter VL l is obtained by means of thecontrol grid resistances and condensersfRGi, CGE., and CG2 connected, respectively, to the grids of theztubes and L2, which resistances and` condensers cause the.y gridbas-,tohecome more-,negative when The s The tubes are oper- The volume'lim- `rent during` the positive half Waves.

theeiect of tube variations. provided to by-pass the alternating current .the :alternating signal voltage.V on fthe grid-Sebecomes `high enough to cause themzto drawcur- When this condition..is..reached,..the power output` ofthe limi ter` |becomes approximately constant regardless. of further increases in the grid` voltage. rihe actualpoint at Whichlimiting occursis controlled by the bias-voltage on the screen grids `SGI and SGLbyfthebiasvoltage on: thecontrol grids-Gir and G2, by the inherent limitationon maximum plate current with aero control` grid `potential and, of course, by the;particular.screen grid and plate potentials.` rlhe desired value of .biaspotential for the screen grids 4is obtained fromrthe potentiometer consisting of `resistances P1, P2. and Ps. The grids GI and G2 are held negative'in the :normal condition by the voltage drop acrossthe `cathode resistanceLS.

The output `of the limiter VL is divided .into two partsby the resistances NI and N5. The .voltage across the resistanceNi is applied to the signal present circuit which, as before stated,

`comprises the highepasslter HPF, input transformer SPT, vacuum tube S. and polarized relay SPR. This circuit responds to the small voltage `d-evelopedracross resistance Nl in consequencerof anysignal transmitted from the transmitting station, which signaLbeing stepped up by `the-input transformer SPT, is applied to the grid ofthe pento-de vacuum tube S, which functions as a rectier by virtue of thenormal positive grid bias andof the `resistance SPg inits control grid circuit. The `high-pass iilter HPF is employed in the signal present channel tosuppress the unwanted frequencies belowv the signal frequency `band which may be present in the bodyof the signal. Since thetourrents-producedby the line noise increase in intensity as they decreasein Vfrequency. the probability of falsely operating the signal present channel from this source is reduced. The signal voltagezacross resistance N5 ispassed thro-ugh the resistance network comprisingresistance elements N2, N3 andNi tothe ,.limiter;` and,-(3 it attenuates` transient disturb- .ances reflected baclr from the lters to such an `extent that they elo-not cause objectionable chatter of relay SPR.

The control grid of the tube Sisnormallyheld positive .bythe1voltageobtained from the potentiometerfmade up of resistances P4 and P5. This .positive bias, together with the reduced screen grid voltage obtained; by the use of resistance SPR!` connect-,edito ,the'sciteen grid of tube S, improves the operation ofthe circuitandV reduces Condenser SP2-is aroundzresistance SPRL Relay SPRhas its :sec-

`onclary, (S), or bias,` Winding connected in the plate circuit of thegtubeLS; Whileits primary'wind- -ing` (P) oroperate, vWinding isconnectedlto Aloattery through the lovv resistance `iiltering `retard Acoil FLT. When there is nosignal presenten the trunkand therefore, no isignal voltage is being :applied .to thefgrid, ofthervacuum tube S, the

. .iBPFf which act .to

plate current flowing through the bias winding of the relay SPR is sufciently large to overcome the effect of the current in the operate winding and the relay remains normal; that is, with its armature resting on its lower contact. But when an alternating current signal is applied to the grid of the tube, theplate current is reduced due to the change in the potential of the grid, and the current through the operate winding (P) of the relay SPR overcomes the reduced current through the secondary winding (S) and causes the relay to operate and move its armature into engagement with its upper contact.

`The plate circuit of the tube S includes retard coil SPI and condenser SPCN. These serve two purposes: first, to reduce modulation products that would cause the relay SPR to chatter and, second, to slow up the operate and release times of relay SPR by delaying the dying down and building up of the plate current through the secondary winding of said relay. These delays compensate somewhat for the fact that there is no band-pass filter in the signalV present channel, as compared, for example with filters BPFf in the signal channels, and aid in preventing the operation of said'signal channels by transients since, as subsequently set forth,

Without the operation of relay SPR, signal channel relay operation cannot take place.

Referring now to the register of Fig. 4, and X wiring in the portion of the receiving circuit shown in Fig.f3, the armatures of relays SPR and CK2 are multiplied together and obtain ground via the back contacts of relay CKI. The front contacts of relays SPR Vand CK2 are also multiplied and connected to conductor J, which extends to the armature of the polarized relay TO. From this relay, this conductor is extended via the armature and upper contact of said relay and the No. 1 contacts of relay CI, which is assumed to be operated in a manner that will be described hereinafter, to conductor L, conductor LI and thence to the operate (P) windings of relays `Rn, Rf. Hence when relay SPR operates in response to a signal forthcoming over the 4rtunk, it applies ground serially over conductors J and LI to the operate windings (P) of all of the channel relays Ra .R12 preparing the same for operation when their associated channels will have responded to the frequencies in the signal as hereinafter set forth. It may be noted that when relay CK2operates as described later,

it has the same eifect as relay SPR, and also that when relay CKI operates, it removes a short circuit from resistance CH2 and thus inserts this resistance inthe ground being suppliedto the armatures of relays SPR and CK2, the purpose of which will be explained later.

When the register of Fig. is used, however,

and Y wiring is provided in Fig. 3, the armatures ever, that the operate windings (P) of the channel relays Ra Rf are connected to conductor` LI, which is connected to the other end of resistance CH2 and to the lower contact of relay OKI, so that it joins conductor L either directly through the armature. and back contact of relay vRa.

CKI when said relay is released, or via resistance CH2 when said relay is operated. Hence when relay SPR operates in response to a signal forthcoming over the trunk, or when relay CK2 operates as hereinafter described, ground is applied serially over conductors J, L and LIY tothe operate windings (P) of all the channel relays Rf, preparing the same for operation when their associated channels will have responded to the frequencies in the signal as hereinafter set forth; y

Since the signal present circuit is connected to the volume limiter VL ahead of the channel lters BPFa BPFf (by virtue of *its connection across the terminals of resistance NI relay SPR will be operated when any signal of sunlcient magnitude is available at the output of the limiter, whereas thechannel relays Ra Rf will be operated only when frequencies passable through their associated channel iilters are present in the signal. Now in any signaling system where speed of transmission is essential to insure the maximum utilization of a minimum quantity of apparatus, and the signals are transmitted under` manual control of a, kind that the signals and the time interval between the signals may not-be of uniform duration, it is necessary to register a received signal as quickly as possible upon appropriate settable register relays connected to the contacts of the channel relays, to prepare the channels for reception of the next signal by releasing the operated channel relays Vimmediately the vregistration is completed, to

connect the contacts of the channel relays to the next settable register even though the signal is still present, and yetprevent a duplicate registration of the original signal on this next settable register. The signal present" circuit, in connection with av circuit controlled by the settable registers as hereinafter set forth, insures the correct performance of these functions by providing means that will cause the operate circuits of the channel relays to remain open once they are opened even though the signal is still present, and will cause them to remain open until the signal is terminated. Y In order to understand how these and other functions are performed, the description of the remaining elements of the receiver will be given in connection with their operation. e

When a sender is seized via the sender-selector apparatus SS and connected to the trunk taken into use by the operator at the transmitting station, conductors 'I' and R of the trunk are connected to the signaling conductors T and R and thence via the sender-selector to leads TI and RI, respectively, of the receiver circuit incorporated in the sender, and operations are then initiated in the sender whereby positively grounded battery is connected to conductors BATI and BAT2, it being understood that suitable sources of current (not shown) have already been or are continuously connected to the filaments of all the electronic tubes of the receiver. Battery on conductor BATI completes an obvious circuit through the secondary (S), orbias, windings of polarized relays CKI, CK2 and CKS thereby causing the energization of these windings but not the operation of their respective relays, the normal condition of each of which may be assumed to be with its armaturel engaged with the lower contact as shown. Battery over conductor BATI is also connected to'resistances A2 F2 in preparation for changes in the potential applied to the screen grid electrodes of the chan'- alliance` nel vacuum tubes Ta Tf. Battery on conductor BAT2 completes an obvious circuit to theprimary winding (P) of polarized relay KPI, but this relay remains with its armature engaged to its left contact because the secondary winding (S) of the relay is also energized from battery D connected directly thereto, completing a circuit over its left contact and armature, normally made Nol contacts of relays KP2 and EP3, conductors 5 and l2, and the lower contacts and armatures of relays Rc and Rf to ground. Battery on conductor BAT2 is also connected to the windings of relays KP2 and KPS in preparation for their subsequent operation as described hereinafter. 1

When the receiving circuit is` thus cut through to the transmitting station at the beginning of a call, there is a brief period during which it may be exposed to speech or noise currents which, if the receiving circuit were ready to receive signal frequency impulses, might cause it to operate falsely and thereby cause a false setting of the rst settable register ordinarily connected to the front contacts of the channel relays. To prevent this, the receiving circuit is normally held in a condition whereby signal impulses cannot be registered until after a definite timed impulse consisting of frequencies c and f is received, which impulse is transmitted from the transmitting station by the operation of key KP thereat which, over its left contacts, causes frequency source c to be applied to conductor SCT and, over its right contacts, causes frequency source f to be applied to conductor SCR. These conductors, across which resistance N5 is bridged to supply a matched terminating impedance for the trunk during the time that it is connected to the keyset KS, join with trunk conductors T and R, respectively, and cause circuits to be completed over the left windings of repeating coil RC. The currents of frequency c and f flowing over this path cause similar currents to be induced in the path including the right windings of the repeating coil RC, the trunk conductors T and R, the conductors T' and R', the contacts SSi and SSz at the sender selector cross bar switch SS, conductors T1 and R1, the front contacts of relay SW, which is assumed to have been operated in any suitable manner, and thence through the pad AP, the left winding of transformer IT with the mid-grounded resistances IN bridged thereacross. The signal voltage thereby developed in the left winding of transformer IT is induced into the right winding, amplified through the limiter VL, and then applied, partly across resistance NI lll ary winding (S) of each of winch is connected in the anode circuit of its associated vacuum tube. The primary windings (P) of these channel relays are connected in series and obtain battery through lter coil FLT. The other end of the series connection of the primary windings (P) of relays Ra Rf is connected to resistance CHI and thence to conductor LI whence it traces back to the upper contact of relay SPR as already shown. y

It has been stated that the grids GI and G2 of tubes Ll and L2, respectively, are held negative in the normal condition by the voltage drop' across resistance L3. The voltage between the cathodes and anodes of these tubes is also partly controlled by the potential drop in resistance L3 but, in addition, is also controlled by the drop in the entire network of resistances L4, L5, L6, Ll and L9 connected to resistance L3, said network being connected to ground through resistance L9, normal contacts of relay SPR, direct to and partly across resistance N5, the former being applied to the left winding of transformer SPT of the signal present circuit and the latter, through resistances N2, N3 and N4, to the input terminals of the channel lters BPF@ BPFf. Since only the filters BPF and BPFf are each tuned to pass one of the two frequencies in the signal c and f, respectively, the voltage thereof is applied to the grid electrodes of vacuum tubes Tc and Tf through resistances Cg and Fg but not to any other channel tubes.

Now each of the channel tubes Ta Tf (which are pentode tubes) is provided with a positive grid bias from positive battery through coil FLT and resistances P4 and P5, and a control grid resistance Ag Fg, respectively, to make each of said tubes function as detectors. Each channel is also provided, as before stated, with its own individual relay Ra Rf, 'the secondground (Y wiring) or through the normal contacts of relay` CKE (X wiring) to ground. Since the battery source is through coil FLT and said battery is grounded at its positive pole and, therethrough, is connected to the anodes of the tubes LI and L2, it is evident that the available potential difference between the cathodes and anodes of these tubes depends upon the condition of the signal present relay SPR. With this relay normal, as would be the case prior to the transmission of a signal, resistances L5 and L9 are serially connected to the common terminal of resistances L5 and L1, the latter resistance being in parallel with resistances L4 and L5. Consequently before the transmission of a signal, the

circuit path for the cathode-anode circuit of both tubes may be traced from ground and battery through coil FLT, resistance L1 in parallel with resistances L4 and L5, resistance L3, through the cathode-anode of both tubes LI and L2 to ground through the upper winding of coil L for tube Ll, and through the lower winding of said coil for tube L2. Atthe common terminal of resistances L5 and L1 there is a parallel branch of this circuit which extends through resistances L6 and L9 to aforetraced ground through the normal contacts of relay SPR.

With the above circuit arrangement it is evident that the potential drop in resistance L3, together with resistance L7 in parallel with resistances L4, L5, will be determined in part by Whether or not the parallel branch made up of resistances L6 and L9 is electrically a part of the circuit by the application of ground 'to resistance L9 via the normal contacts of relay SPR. When this relay is normal, the drop across resistance L3 plus the drop across resistance L'I in parallel with resistances L4 and L5 is larger than when the relay is operated because, in the former case, the parallel network of resistances L1 and L4, L5 will draw through itself not only the current which traverses the path including resistance L3 to ground through the cathode-anode of the tubes, but also the current which traverses the path through the parallel circuit including resistances L6 and L9 to ground. When relay SPR operates, this latter parallel circuit is opened and, therefore, the full voltage of the battery is then available only for the network of resistance L1 in parallel with resistances L4 and L5 serially through resistance L3. Hence the voltage available across the cathode-anode of each ofthe tubes Ll and L2 is less when relay SPR is normal alien-fle 1l than when it is operated. lThis means, of course, that the amplication ceiling of the limiter tubes LI YandLZ is lower when relay SPR is normal and higher when it is operated.

AIt will further be noted that the potential applied to the screen electrodes SGI and SGZ of the tubes LI and L2, respectively, is controlled by the potentiometer made up of resistances P1, Pg, and Ps to ground at one end and to the terminal of resistance L'l on the other, The value of the resistances P1', P2 and Ps is so computed that the potential available at the screen electrodes SGI and SGZ kwhen relay SPR is normal will insure maximum ei'ectiveness of tube operation for the potential difference then available across the cathodefanode Aelectrodes of these tubes. When relay lSPR operates, the potential at the upper terminal of resistance L'l is, of course, different andhigher than before, so that,'by virtue of the current now drawn through the potentiometer to ground, the potential available at the screens is higher and of the correct correlated value to insure'maXi/mum ampliiication with the cathodeano'de potential difference then available across the cathode-anode electrodes' of tubes Ll and L2,

Thus, `by 'virtue' of the control exercised by the parallel branch L5, L9 of the above circuit network, the amplification ceiling o'f the Volume limiter may be alternately raised and lowered with the operation and release, respectively, lof relay SPR. And by virtue of the potentiometer Pi', P2 and Ps, the screen potential vapplied tothe tub'esof the amplier will also be raised and lowered'with the operation and releaseof relay SPR to vthe correct values required for the voltage applied in each case across the cathode-anode of each tube of the limiter.

Returning, now, to the operation of the circuit, the `operator Will'depress the Ikey KP before depressing vany ofthe digit keys. It may be assumed'that the key contacts will chatter for a vbrief interval before making a solid closure and that, during the chattering period, the transient voltage produced by the 'application of signal frequencies c and f (or any combination of signall frequencies) through the contacts Will be applied to the line. rihisvoltage will, of course, be applied to the control grids GI and GZof the Volume limiter `and will be amplied thereby, some `of the 'amplified voltage being made available lacrossl resistance NI and thence across transformer SPT to cause the operation of tube S and the consequent operation of relay SPR, and the rest of the amplified voltage vbeing available 'across the network N5, N2, N3 and Nfl-.for application to the channels. However, it will take some time to operate relay SPR after a part of the transient voltage is applied to transformer SPT, and this time definitely exceeds the duration of the transient. Consequently, during the time that the transient voltage is applied to the receiver, the amplifying factor of the limiter is at the lower ceiling xed by the voltage across l2 odeand anode'V is made larger n y to the cathode of the'full negativepotential'bf theb'attery through the c'oniparatively'low resist'- ance coil FLT andr'esistance Lil", H

The transient voltagey generated'by the chat-- tering of the Contact keys will be followed by theV steady voltage subsequently available lthrough the key contacts. But subsequent to the termi- V nation of the transient voltage relay SPRV operthe cathode-anode electrodes of its tubes LI and L2 as determined by the potential drops in re- 'sstancs L3, and L1 in parallel with resistances L5 and L4, and resistances LS and L9 in series with said parallel combination, And although the Vtransient voltage is amplified, yet the ampliii'cauon level is below that which is necessary to operate any of the channel tubes T-.. Tube S, however, does operate on the portion of the amplified transient'voltage made available across esistanc'Nl because its sensitivity is higher, dus to' tnera'ct ytnatthe 'voltage across its' cathates, either as a censequence of the duration' of this voltage or as a consequence of its duration; plus the duration of the pure signal voltage that follows. With the operation of relay SPR, the ground connection to resistance L9 is broken', and -for the reasons previously advanced, the' voltage acrosskthe cathode-anode of each of the volume limiter tubes Li and L2 is now raisedandth'e" potential at the screens thereof is appropriately altered, both thereby raising the ampli'catio'n ceiling of the volume limiter to `the fullv value required for channel response to the undistorted signal voltages.

It will be noted that the serial networko'f condenser CC and resistance L8 is joined'Y at the common terminal of resistances L6 and L9 and that condenser CC is grounded.- This. network is provided to insure that the increase in amplification of the volume limiter subsequent to the operation of relay SPR takes place gradually in order to avoid the production of other obec'tio'nable transients by Vvthe sudden rise` in current.

During the time that relay SPR is normal,

ground is applied to' the right terminal of resistance Le and since the value of this resistane Lil is low compared to that ofresistance L6, condenser CCis practically in the unchargd state. Upon the operation of relay lSPR subsequent to the dissipation of the transient voltage applied to the line, ground is disconnected from the right terminal 'of resistance L9 and a charging circuit is established for the condenser-ek- Y tending from battery through the winding of coil FLT, resistances Le, L5, L6 and LB'Ii-n series, condenser CC to ground. vDuring the time' that the condenser is becoming charged,` the potential at the upper terminal of resistance L1 Vgradually rises and the` diie'renc'e of potential betweenv the cathode's kand anodes of tubes LI and L2 is gradually increased until the condenser is e` fully charged, at which time said diirerence oi potential is increased to the full value requiredffor high ceiling ampliiicatin.

Returning, no-w, to the operation of the receiver, when the operator depresses key KP and the transient voltage developed by the chattering of the key contacts as above setforthy is fully dissipated, a part of the undistorted Asignal volt-` age derived from the signal frequencies Gand` f is applied to transformer SPT to cause the operation of tube `S and that of its anode relay SPR which, upon operating, applies ground to conductor J vand vthence to conductors L and/'or L1, resistance Cil-ll and the primary windings (P) Iof the channel relays Rd Rf, while the remaining voltage is applied (through the respectivekters EPFL. and BPFr) to the grid electrodesof tubes Tc and Ti," respectively. The application of the latter voltage to the grid electrodes reduces the value of the positive potential between grid and cathode normally thereon from battery through coil FLT and network P4 and P5. 4In consequence, the respective'anode currents flowing through Vthese .tubes and the secondary (S),

duced, causing these two relays to 'operate' n` by the @pregate eier-alma theburrent through their operate windingI (P), the circuit of `which may be traced from battery through the filter FLT, serially through the primary winding (P) of all the relays Ra Rf, resistance CHI and thence as already traced to ground on thecontacts of relay SPR. It will be noted that the current which causes the operation of relays Re and Rl, while I:(lowing through the operate winding (P) of all the channel relays as well, yet will only cause the operation ofthe two relays Re and Rf. The reason for this -is `because vthe current in the secondary (S) winding of each of the'other channel relays has not been diminished by any material A)alteration in the control grid potentials of" their respectiverassociatedtubes.

With relays Rc 'and R'f thus operated, ground is disconnected from conductors and i2, which remove ground from the secondary winding (S) of' relay KPl, the path ofthe ground being by way of the No. 11 norm-ally made continuity contacts of relays KFZ and XPS and through the armature and left contact of relay KPI.

Relay KP! now operates slowly over an obvious circuit through its operate (P) winding, the slowness of its operation being due to the charging current for condenser KPC flowing through itssecondary winding (S) and resistance KPRl, which current opposes' the current flowing through the primary (P) winding. When the condenser KPC is completely charged, the current flo-wing through the winding (S) ofthe relay is limited by the high resistance KPB, and since' the resulting" magneticflux is smaller than that 'produced by the current flowing through thdprirn'aly (P) Winding', the' relay is caused to operate. Y

Resistance KPR is providedtoinsure thatthe armature of relay KP'l shall always engage its left Contact when the circuit is idle. If this resistance were omitted, the removal of battery from conductor BATZ during the time between the break-ing or the left Contact of relay KP! and the operation of relays AKP? and KP3 would leave the circuit blocked since condenser KPC would be charged and no current would be nowing in the secondary winding (S) of relay KPI to-.release it.

Now when the KP signal is terminated by the' release of key KP after the required interval to operate relay KPi, or by anyother suitable means `such as, for instance, a simple timing circuit responsive to the depression of key KP and adapted to keep frequencies c and f on the trunk conductors for the required interval, therrelease of either relay Rc or relay Rf will cause ground to be connected to conductors 5 or l2, respectively. Since these two conductors are joined at the No. 1 normally made contacts of relays KPZ and KPS, and since relay KP! is now operated, the ground on conductor 5 or i2 (or both) is applied to the windings of relays KP2 and KPS via thearmature and right contact of relay KPl. Since battery is connected to the other terminals of the windings of each of these tWo relays by conductor BATZ, both relays will operate and lock to ground on the No. 'contacts of relay KPZ'. (The No. l front contacts of relays KP2 an-d KPB maintain the ground via the armature'and contact of relay KPI as relays EPZ and KPS operate.) Relay KP2, over its No. 8 front contacts, now reapplies ground to the secondary winding (S) of relay KPI, increasing the current flow therethrough in consequence thereof and causing relay KPI 'to release and reestablish its 'armature into engagea ment with the left contact.

Relays KPZ and 'KP3, upon operating, perform:

the general function or extending theupper cone tactsoi the channelrelays Ra'. ,Rf to conduce tors A F, ve of which, in the register of: Fig. 4, 'extend through contacts on a previously operated steering relay TR! to the lowerwindings of the relays of the rst digit'register inf which the rst operations of the relays Rc'. Rf'

in the proper combinations will be registered. In the register of Fig. 5 an extra translating step isV required, as explained hereinafter, so the six registering conductors A F are connectedl directly to the windings of six translatingl relays, the conta-cts of which are connected through contacts onra previously operated steering relay AC to the lower windings of the relays ofthe rs't digit register. quent operations of relays Rc ltr I-i'nfthe proper combination will be registered in the first and succeeding groups ofregister relays. Relays when the circuitV is in this condition the screen grid potential of each channel tube T is changed when the corresponding channel relay operated whereas in the original condition the `operation of the channel relays has no such effect. In addition, relay KP3, over its No. 7 contacts and conductor I8, supplies ground to the serially-connected tertiary windings (T) of all the channel relays Ra Rf. These tertiary windings are poled to oppose the primary windings (P) of said relays and, for certain operations described hereinafter, function to release the relays.

As previously indicated, it is necessary that frequencies c and f be received for a denit'e length of time without frequencies a, b, d ore, if' the circuit is to unlock; that is, if relay KPI is to operate and relays KPZ and KPS are to operate in consequence of the operation of relay KPI. If an impulse containing one or more of these latter frequencies should appear at any time before relays KPZ and KPS will have been operated", the corresponding channel relay, or relays, will, of course, operate and apply ground to the secondary winding (S) of relay KPI and to condenser KPC via the No. 4 and No. 6 back contacts of relays KPZ and KP3, or any of them.. This ground restores the full bias current to the secondary (S) winding of relay KPI, and if this relay had already started to operate (because, say, or the presence of frequencies c and f in the extraneous impulse along with the other frequencies), it will restore immediately because of the iull bias current produced by ground on the With either arrangement,y Subsc-f themselves only for the necessary length of` time, since, with relays KP2 and KP3 normal, the front contacts of the channel relays are not cut through to the register, and the channel relays themselves whch were operated by the impulse will restore when the impulse is terminated since, with the removal of the grid potential from the associated tube by the termination of the impulse, the full plate current is restored which, owing through the secondary winding (S) of the associated channel relay will cause the latter to restore. It will be noted that during'these operations, the screen grid electrode of each tube remains grounded through appropriate contacts of relays KPZ and KP3 and, therefore, will have no effect upon the intensity of the plate current when the signal potential is removed from the grid. That is, prior to the reception of the KP signal, the channel relays Ra Rf are free to operate and release in acccordance with the application and removal of the incoming alternating current signals. The reason for this is because the screen grids of the several channel tubes, being grounded at ther contacts of relays KPZand/or KP3, are powerless to change the intensity of the associated plate currents when the latter increase to their normal strength upon the removal of impulse potential, in consequence of which the several channel relays restore to normal in response to the preponderating bias current flowing through their respective secondary (S) windings. After the KP signal khas been received, however, and relays KPZ and KP3 have been operated in consequence thereof, the direct ground formerly supplied Via some of their back contacts to the screen grid electrodes of all the channel tubes is removed and these electrodes are then connected to ground only as long as their respective channel relays remain on their back contacts. The result is that, when `a channel relay operates, the screen grid potential of its associated vacuum tube is changed in such a way that the relay is locked up. This locking action is caused by the fact that when a channel relay operates, after the anode current flowing through its bias winding (S) has been reduced sufficiently -by the incoming signal, the operated relay, by causing its grounded armature to break with its associated back contact, removes ground from the screen grid of its associated vacuum tube and causes the latter to be connected to a potentiometer which supplies a much lower voltage than normal between screen grid and cathode, in consequence of which the plate current of the tube remains reduced after the signal has terminated and the control grid electrode has been restored to its normal potential. Y

Thus if we assume that a signal made up of frequencies a and b is transmitted before the KP signal of frequencies c and f and, therefore, before relays KPZ and KP3 are operated in consequence of the latter signal, the signal voltage due to the signal composed of frequencies a and b is applied to the control grids of channel tubes Ta and Tb, respectively, and the current through their respective anode circuits (including the secondary (S) windings of relays Ra and` Rb) is reduced and relays Ra and Rb operate on the current flowing serially through their primary winding. When operated, relay Ra opens one of the two paths by which ground reaches conductor I9, and relay Rb opens one of the two paths by which ground reaches conductor It. However, since relays KP2 and KP3 are normal, ground is `still Vapplied to the screen grid electrode of tubes Ta and Tb via conductors I9V and I4, respectively,`

over contacts 8 and 5, respectively, of relay KP3. The presence of ground on these electrodes will causethe reduction of the anode current to be determined exclusively by the potential of the signal applied to the control grids of the respective tubes.

so that, when the signal ceases, the anode current is restored to its original value and relaysRa and screen electrodes of their respective tubes Ta and the No. 5 contacts of relay KFZ.

Tc. VWith ground removed these electrodes are connected to a potentiometer made up of resistances A2 and C2, A3 F3, and the (P) Windings of relays CKI CK3, as follows: Resistances A2 and C2 extending to battery over conductor BATI, while resistances A3 and C3 eX- tend to ground via a circuit consisting of the serially connected primary windings (P) of relays CKI, CK2 and CK3 shunted by the four resistances B3, D3, E3 and F3 in parallel. The potential applied by this network t0 eachofthe screen grid electrodes of the tubes Ta and Tc is lower than that available thereto by the previous ground connection and this will cause a further .reduction in the anode current. When the signal voltage ceases, the control grids are restored to their normal positively biased state, but since av low potential is still available at the screen grid electrodes from the'potentiometer network, the anode current is still reduced in spite o,f the restoration of the control grid electrodes to their normal state, thereby causing'relays Ra and Rc to remain in an operated condition until their operate (P) windings are opened.

It will be noted that when relay KPZ operates, it applies ground over its No. 8 contactsto the secondary winding (S) of relay KPI and to condenser KPC in the same way as the channel relays Ra, Rb, Rd, and Re when and if they, or any of them, operate on an alternating current impulse prior to the appearance of the timed KP impulse composed of frequencies c and f. This ground causes relay KPI to release and, condenser KPC to discharge as above described, but

the release of this relay does not interfere with the operated condition of relays KP2 and KP3 since these relays are now locked to ground on The purpose of this arrangement is to make sure that the timing circuit, comprising relay KPI andY condenser KPC, is normal and ready to give a complete timing cycle on the next call. A sequence adjustment of the No. 5 contacts of relay KFZ insures that these contacts close ahead of the No. 8 front contacts which release relay KPI.

As already stated, the alternatingV current signal code impulses consist of various combinations of two frequencies a f transmitted simultaneously according to the code previously given. In the receiving circuit, each frequency (after the transient voltage is dissipated and the ceiling of the volume limiter VL is raised as previously described) nds a path through its corresponding filter to the grid of one of the vacuum tubes Ta Tb and causes the operation of the associated relays Ra Rf. After the operation of relays KP2 and KP3 by the KP impulse signal which, as above noted, is transmitted f, say frequen-v .primarywindings (P). Aafter 'the transmission ofthe KP signal and,

ahead of the digitalimpulse codes, theoperation .of one or more of relays Ra Rf causes ground itc be applied to the corresponding conductors A F which connect with the settable registers or the translating relays associated therelwith, causes ground-to beremoved fromthe cor- ;responding resistancesA2 F2 to reducethe `Voltage on the `screen `grids of the associated vacuum tubes, causes the operated channel -relaysto lock in consequence thereof as already described and, further, allows current to ow lthrough the primary windings (P) of relaysCKl, CK2 and CK3 in an amount almost directly proportional to the number of relays `Ra ARf -which are operated. It will be noted that, prior to the reception of the KPsignal, relays CKI,

HCK2,.CK3, cannot function because they are, in

effect, short-circuited by ground supplied to leads v(5, `8, I6, 54,15 and I9 from the back contacts Vof relays KP2 and KP3.

Relays CKl, CK2 and :0K3 are all polarized relays. The operate current through the respecztive primary windings(P) and the bias currents through `the respective secondary windings (S) are so proportioned that :none of them will operate `when a single channel relay Ra, Rf is 44operated. Relays CKI `and CK2 will operate,

however, when two of said channel relays operate because of the'increase in current through the primary winding (P), and relays CKI, CK2 and CK@l will operate Vwhen three orrmore of said vchannel relays operate becauserof astill higher increase'in the current through their respective Thus, for example, if,

therefore, after the operation and locking of reylays-KP? and KP3, the operator were to depress the f digitkey 1 to'put forth upon the trunk an impulse consistingoi frequencies a and d, said impulse would cause the operation of relays Ra i and Rdyin consequence of `which ground would .-beremoved from the` screen grid electrodes of `the primary windings (P) is determined by the ohmic resistance of said separate windings and Y-lcy the number of parallel pathsto battery BATI whichwill be formed through resistances A2, A3 F2, F3 by the operation of the number of channel relays. In the-case assumed, relays Ra and Rdare operated; consequently, the current through the primary windings (P) of `relays CKE, CK2 and CKS is determined byresistances VA2 and D2, and A3 F3,the actual path tracing from ground, serially through the primary windings (P) of relaysCKl, CK2 and 0K3, with resistances B3, C3, E3 and F3 in shunt therewith to ground, resistances A3 andA2 to battery BAT! and,` in parallel therewith, through resistances` D3 and lD2 .to battery BATI. The quantity of `current flowing through this circuit will produce suicient magnetic flux in therelays to overcome the` flux due to the current ilowing through the ,secondary windings (S) of relays CK! and CK2 and will cause said relays to operate, but this current will not produce suiiicient uX to overcome `the current through the secondary winding (S) of relay CK3 which, on this account, remains unaffected. Relays CKI 4 audlCKZ willremain l operated untilmground isreapplied to conductors :i9 and I0 lon the release of` relays 5R11; andfRd, Awhich will be described later.

Should therebe three frequencies in adigital impulsesay frequencies a, d and c, then relay Tc twill Yoperate ,along with relays Ta and Td, and ground will be removed from` one `side of resist.- ances C2, C3 whereupon the circuit ci relays CKI, CK2 and CKE willrtakeon an additional` parallel `branchthrough\ resistances C2,V C3 1to `battery BATL Vresistance being removed `asa shunt Larouild `relays CK! CK3, 4and the current flowing through the primary windings (P) of relays CKS, vCK2 Iand 0K3 :will be increasedso that,` thistime, the fluxwill be sufficientto overcome fthe uxduetothe current flowing through `the secondary winding (S) of relay CK3, ywhich will now operate along with relays CKI and CK2. rRelaysjCKl, CK2 and GKS, therefore,serve.to v,check each of the incoming. signals and,l as willbe shown,gwi1l,advise `the sender whether ornoteit Ashould register these signals.

VConsidering the operation :of the receiver :in connection with the settable registers of Fig. 5 (and Yywiring `in Eig. 3) the `operation of relay CK2 removesground yfrom conductor Mend applies itntoconductor J in parallel withthe vground `applied to, this `conductor byrelay SPR. Relay. CKI, whenoperated, removesa short cir,- 4cuit :around resistance CItZand` effectively adds n.this resistanceinfserieswith the primary windings ,(P) Aofhthechannelrelaystd .-Rby inserting said resistance betweenconductor `LI and conductor L, the-latter .joiningtconductor J atythe contacts of relay APT. Withrtheprimary windings (P) of relays Ra Rf connected through resist- .ance :CI-Il to ground,the circuitchas its VfullsensitiVity, but after relay CKI operates andresist- `(ance CH2A isinsertedin series` with fresistanceCI-I I .the sensitivity is somewhat reduced. :Thereason for thisslight decrease'in sensitivity is to Vincrease A*the protection against false operations o n i transients and cross-modulations `which may :appear in the, unoperatedxchannels. Relay CKI also applies -ground from .relays SPR` and/ or` CK2 via conductors J and'L as tracedV above,to conductor -H,in consequence of whichra circuitiscompleted for relay TG over its No. 2 normally made conltinuity contacts,` causing said relay tooperate and rlock over its No.-,2 front contactsto groundson conductorl J. VRelay TG :performs Aa `function which '-willcbe shortly described.

:As ypreviously indicated, the path between con- -`ductor Jand conductorL-Aisclosed inthe sender lat fthe start` of each digit `and remainsclosed until the sender opens-it, afterthe registration Aofeachdigit, by theoperation of relayPT, as hereinafter described, whereupon `the channel relays are `released by'virtue of the .fact Vthat the 4circuit of the primary windings (P) ofrthechannel'relaysis opened at-.the contacts ofyrelay1PT. fOncethis has occurred,` thepath=tofthepri1nary `windings(P') of `the channel `relays remainsfopen and the. channel relays y remain released until-re- 1lays :SPR and CK2 `rboth :release and remove .ground -from conductor 5,-. since, luntil thisv occurs, relay TG remains locked to :preventthe release ,of relayPT. rIt willzbe noted, .however,t1hat, although the path ;to theprimary windings .(P) is opened at the contacts of `relayPTI,u the operation of relay .KPB has appliedground over ,its No. 7 `contacts to conductor i3 whichis connected` serially to the tertiary winding (T) ,of the, channelirelays, the, circuit thereof being corn- .pletedto batterythrou'gh retard coillLlI.V 'Now 'gnam 'consequence of the current flowing through their of the channel relays when current is alsoA flowing through their primary windings (P), the combined effect of the reduced current in the secondary winding (S) of the relays affected by a signal frequency and the current flowing through their respective tertiary wind--4 ings (T), will not be suicient to overcome the current owing through their respective primary windings (P). Consequently said relays will remain operated until the primary circuit is opened at the contacts of relay PT. Those channel relays which do not have a signal voltageapplied to the grid of their respectively associated channel tubes will have full current flowing through their respective secondary windings (S) so that these relays will remain in a released condition. Prior to the operation of relay PT as described hereinafter, the ground applied to conductor J over the upper contacts of relay CK2 insures that the digit will be registered correctly on short pulses. that relay CK2 is held up by the locking circuit of relays Ra Rf, as previously described, while the ground through the upper contacts of relay SP-R insures that there is no double registration in case the incoming signal persists for a longer time than actually required for registration; that is, for a longer time than it takes relay PT to operate.

' The registration in the sender of the succession of signal impulses transmitted from the transmitting station by the depression thereat of the digit keys of the key-set KS subsequent to the depression of key KP, depends upon the construction of the sender, the character of the seta sender which, for instance, may be located in oice X for the completion of a connection to a `local station C, or to a telephone station B, the

latter being located in office Y. If these stations are also to be reached from a call originating in' office X through an operators position provided with facilities for keying a series of direct current pulses representative of the called station designation, then the sender must be provided with corresponding facilities to register alternating current pulses when the call originates from an alternating current key-pulsing station and to register direct current impulses when the call originates at a direct current key-pulsing station. The register for a sender adapted to handle both types of calls is illustrated in Fig. 5 and will The reason fory this is the fact 2() be considered hereinafter. Fig. 4, on the other hand, shows schematically the portion of a sender, which, for instance, might be used v'at-oiice X for completing calls to a subscriber in that office only, such as subscriber C, when it is not necessary to accept calls from operators equipped with direct current key-sets or to completercalls to other oiiices, such as oilce Y. One of the characteristics of this register circuit, as compared with that of Fig. 5, is that it must always be supplied with a full complement of digit signals and that, having received them,` it tells the `sender to proceed with the call without awaiting for an ST or start signal to be transmitted or regis'.- tered. Since such a signal may be received inadvertently, however, the register has been arranged to ignore it unless it should appear before the full quota of digit signals has been received, in which case a reorder indication will be given. These and other differences permit certain simplications to be made in thisl case, which will be apparent from the more complete descriptions of the two arrangements that follow.

Considering rst the registers of Fig, 4 (X wiring in Fig. 3) and assuming the same to be incorporated in a sender adapted to register only alternating current impulses of the character described (in which event relay SW will not be provided and conductors TI, Rl will be connected directly to the input terminals of pad AP), the seizure of the sender at the sender selector switch SS and the connection of the sender with the trunk will initiate circuit operations among which are, as said before, the connection of battery to conductors BAT! and BAT2, and the operation oi the steering relays TRI and TRA by the momentary application of ground to conductor 25, whereupon both of these relays lock serially to ground on the left contacts of relay 'IRA while relay TRI is furnished with a supplementary holding path over its No. 6 front contacts and conductor H to ground on the upper contacts of relay CXI when the latter operates on the regular digit pulse. At the same time the other pairs of steering relays, TRB and TR2, TRC and TRS, etc., up to the nal pair TRN and CLofwhich only relays TRB, TR2, TRN and CI are shown, for the second and succeeding registers, are operated, one from the other in succession until all of them are operated and locked up. With the operation of re1ay TRl, the five signaling conductors A E (conductor F has a different connection in a settable register of the kind shown in Fig. 4) are connected, respectively, to the operating windings of the ve relays I 5 constituting the registerI for the rst digit. After relays KPZ and KPS have been operated byA a KP signal, obvious circuits are completed from ground on the upper contacts of the channel relays Ra Re operated in combinations of two according to the code given, over the appropriate two of the five conductors A E, two armatures and right front contacts of relay TRI to the lower windings of the two corresponding Vrelays of the ve register relays I 5 of the rst digit register. When the first digit is registered and relay CKI is released,- relay TRI is released and the signaling conductors A E are advanced over back contacts of r-elay TRI and `front contacts of relay TR2 to the operating windings of the relays I '5 of the second digit register. At the same time, the operated relays in the rst digit register are locked up to ground on the No. 7 normally made contacts of relay TRI, and conductor' H is extended fanta-rst 2'1 l"to relays TR2 and TRB. i"Similarlyfwhenithe "second digitl is registered and relay CKI is -rel'eased, `relay TR2 releases and the five signaling `conductors A E andconductor H areextende'd to the third group of steering and register relays,

tration will be stopped and a reorder signal will i.

besentback to the transmitting station as van'in Idication of ari-error which must Mbe Acorrected by retransmittingjthe whole number,

With this register arrangement, the registra- :tion of each digit is indicated by the noperation of two relays "in a particular register an'dit is possible to give a denitedndication that the registration is completed, which may be ,accomplished `by means of `polarized marginal relay TO which operates over its .primary winding (P) f as soon as two register'relays of the'connected register close their locking circuits, as shown hereinafter, butwhich will not operate when `only one relay of said register operates.

Thus `when a digit signal comes' in, say the `signal of digit 9, the-pulse code .of which isfrequencies aand e, relay SPR' operates to supply operating ground to the operate windings (P) ofthe channel relays Ra .'Rf. Relays Raand `Reopera'te and lock in response to thefrequencies inthe signalgand relays -CKI and "CK2 also operate for the reasons already given. Ground iL-llled to conductor H by relayV CKI short-circuits relay TRAwhichreleases and thereby re- -rnoves'the ground it wassupplying'tothe wind` No. i front contacts of relay HP2, conductor E,

No. 5 front contacts of relay`TRI,` lower winding of relay 5 to battery. Relays I and 5, upon operating, close a path from battery through their l Arespective upper windings and locking contacts, 'No 7 front contacts of relay TRI, right contacts of relay TRA, winding (P) of relay TO, contacts of -relay CKA, conductor K, lower contactscof relay CKS, which is norinal since only twdfre- @quencies are present in the signal, to ground. `Relay TO operates, disconnects the resistance Vgroundrbeing supplied overconductor J Afrom resistance CI-I2 nvia the front contacts of relay *SPR and/or relay CK2, to the operate windings (P) ofthe channel relays, and locks 'itself to fsaid-ground on'con'ductcr 4J via its armatureand -front contacts, secondary lwindings (S) V'to loattery 'via contacts No. 2 of relay CI. (Since both the (P) and the (S) windings of lrelay TO cause vsaid relay to operate, a biasing spring or other suitable means Amust be provided to release it.) A#It the signal is short' and Jrelay YSPR releasesbe- ,foreregistration is completed, relays Ra and 'Re Mare, ineverthelesa held operated by the ground Circuits are supplied i to conductor-CJ )through resistanceCHZ (and the upper contact of relay'CK inutil-.relay TO operates to `signify that the :registrationlif the digit has taken place. If thersignal remains. 'on longer `than the time required Lfor theregister relays and relay TOto operate,thefchannelirelays Ra andvRe release but relayTOywhichihas been `locked fup as previously described;` remains operated until relay SPR releasesfatthe :endcof the Vsignal pulse.

`When the channel relays VRatand Rersrele'ase, relays CKI andCKZ .release'also, the formerldis'- connecting; ground from conductor totcause the release of relay TRI which, in consequence,

i advances `the signaling conductors A `over its Nos. l 5 back contacts, respectivelyto the armatures of theNos. 1 :.contactsxrevspectively, of the next Ytransferrel-ay TR2. from V,which they are `extended via the .front contacts of that relay to the register relaysloflthe-:second digit register. The release of frelayTRtialso advarices ,conductor Hover itsNol 6 back' contacts and the No. 6 front contactsof relay .'IRZlto'the winding of that relay, and relay TRBl.and,.in:ad dition, relayfTRI at its No. l7rcontacts, opens'ithe connection from `.thewinding KP) :of relay T Orto the first'digit register v,and `provides la ground? for locking the two operated Vregister relays: I and in that register. `The register circuit is rnow ready for vthe second digit signal, 4after the .reception of which `itachzances to the thirdldigit registerfand so on until all of the digits have .been registered. When ground is removed 4from conductor at the end of the final digit signal, relay .CI isreleased., and since Aitopenslead L` at #its UNO,A lcontacts and, therefore, lead LI,` furtherioperation of relays Ra Rf in the'freceivingcircuit:is prevented. kRelay'Cl, throughitsrNo. 2 contacts, also opens the locking battery for `relay. TO .and by means of contacts not shown causes the sender to advance the call.

Should only one channel relay operate `dueto the presence of one yfrequencydin the :impulse produced, say, by some abnormal-condition, the corresponding register relay would operate falso, but the latter would not lookup-sincefwithrelay CKI release-d, no ground wouldlce applied :taconductor H and relay TRA would not releaseiinlcon sequence thereof and Ano locking circuit .forthe register relay would `loe `available, .throughlthe primary winding (P) of relay TO. Should more than two channel relays operate, then relayCKS` `would operate in addition to relays CKI andCKZ for the reason already advanced and relayCKL upon operating, would apply ground-to conductor RO, completing thereby ak circuit to a suitable reorder" circuit which would function to cause the reorder signal to be sent back to the transmitting station, in meaning of which, to the operator `thereat, would be to retransmit the entire number. Relay'CK3, by breaking its lower contact, disconnects ground from conductor --K--to prevent relay TO from operating.

Relay CKA, which'is of the slow-release type,1:is normally operated by groundonconductor'M applied thereto through the back contacts of relay CK2. It is released when relayCKZ operates, and serves to delay the closing of the register locking circuit and hence the operation of relay for a short interval in order to allow ample time for relay 0K3 to function in case one or more interfering frequencies should cause the-operation lofmore than the two Achannel relays kwhich `would `vbeoperated by a normaldigitimpulse.

23 Fig. schematically shows the registering elements of a sender in which each of the digit registers comprises four relays instead of ve. A

`Vsender of this type is available not only to the trunked connection from the distant transmitting station Where alternating current keying is used, but also to a local operator at office X whose position is equipped for direct current keying of impulses by which to obtain the number of the called station as, for instance, the position typied by the cord CD equipped with a key-set DA, and the `local trunk designated by the jack LJ. The impulses produced by the key-set DA are direct current impulses which are registered in what is essentially a four-unit code as compared with the `direct live-unit code of the alternating current signals for the registers of Fig. a and, for a sender which must handle digits transmitted into it by either code, either a different set of registers must be provided for each code or one set of registers for both and a translating arrangement by which one code is changed into the other. For practical reasons the latter, or translating arrangement, is shown, and since the direct current pulse code is the basic one, the alternating current signal indications are converted into equivalent direct current pulse indications, the digit registers taking the direct current pulse code setting for the same digit whether the digit is transmitted by direct current pulses from the key-set DA or by alternating current pulses from the key-set KS.

The translator comprises the six relays TA TF shown in the lower part oi Fig. 5 but only a portion of their respective contact equipment and interconnecting wiring is shown. The six translator relays TA TF are operated by the channel relays Ra Rf over conductors A F, respectively, when the latter relays operate after the KP signal has been received and relays KPZ and KP3 have been operated in consequence thereof, relay TA being operated by relay Ra, relay TB by relay Rb and so on up to and including relay TF which is operated by relay Rf.

In order to simplify the understanding of the operation of the translator, the table below is furnished to show, for each digit, what combination of translator relays is operated in accordance With the alternating current signal code and what register relay or combination of relays is operated thereby, these register relays being the same for signals in accordance with the direct current pulse code, which cause their operation by means of suitable indications placed on conductors TP, TM, RP and RM by the direct current key-pulsing circuit DCP.

t Leads Di it Translator Digit Register Grounded For g clays elays Direct Current Operation It will thus be seen from the above table that, with the vfour-relay digit register, the number of relays operated to indicate the different digits 24 varieswfromnone -for the digit 0 to three for the digit 8 when relays l, 2 and 5 are operated. If the relays are given appropriate numerical designations, this system has the advantage that the digit itself may be identified by adding up the designations of the operated register relays. It lacks, however, the positive indication that the registration of a digit has been completed, which is obtained with the five-relay digit register of Fig. 4 wherein two relays', and only two, are always operated per digit and a relay TO is made to respond to this operation. As a consequence, it is not possible to use a marginal relay TO, as in the register of Fig. 4, to indicate that, the register is satisfied, but a timing circuit must be used to insure that the channel relay circuits to the several register relays are maintained long enough for the slowest relay of the register to operate. The timing interval is obtained from polarized relay PT which is made slow-operate by means of the condenser PTC and resistance PTR associated with the right winding (R) of the relay, to the joint terminal of both windings of which battery is connected, through the left contacts of relay ACP which, along with relay 0N, is operated in any suitable manner when the sender is seized for use on calls using alternating current'key pulsing. As long as ground is supplied vto the right winding (R) over conductor M via the No. 1 contacts of relay TG from the lower contacts of relay CK2, relay PT is held in the released position by the current owing through said right winding (R), during which time condenser PTC is, of course, short-circuited. But when ground is removed from conductor M by the operation `of relay CK2, a charging circuit for condenser PTC is established from ground through resistance PTR, condenser PTC, right winding (R) of 'relay PT to battery on the left contacts of relay ACP. The charging current .of Vthe condenser is in the same directionl as the current produced by the circuit completed by ground on conductor M so that, during the time that the flux produced by the charging current predominates over that 'of the current flowing through the leftA or operate winding (O) ofthe relay, the armature of said relay remains engaged to its Contact to maintain ground to the operate windings of the channel relays via conductor LI, resistance CH2, conductor L, contacts of relay PT, conductor J to ground on the upper contacts of relay SPR and/or the upper contacts of relay CK2. When, however, the resulting flux drops below that due to the current flowing through the left winding (O) of relay PT, said relay operates and disconnects ground from the operate winding (P) of the channel relays with consequences already noted inconnection with the register shown in Fig. 4. v

The relays l, 2, 4 and 5A of the individual digit registers are operated by grounds on conductors TM, TP, RP and RM, respectively, while the steering relays AC and AL, corresponding, respectively, to the relays TRI and TRA of the register of Fig. 4, are controlled by ground on conductor TS. Relays AL andrAC are operated in series by momentary ground on conductor 20 and locked up to ground over the left contact of relayrAL, and at the same time the other pairs of steering Vrelays (not shown) between AL and AC and the steering relays NL and NC for the final register are operated, one from the other in succession, until they are all operated and locked up. With relay AC operated the conductors TM,

manner until the incoming start signal trans-4 mitted from the transmitting station by the depression of key ST thereat indicates that the last digit has been transmitted. rThe ST signal perates translator relays TE and TF, in turn operating relays I and 4 of a register succeeding the register which has taken the registration of the last digit transmitted (the number of digits which may be transmitted may vary depending upon the Vroute and the called oice) and a circuit closed through a pair of operated contacts on relays I to 4 of any register will operate a start circuit (not shown) which advises the sender that no more digits willbe forthcoming and that, therefore, it may proceed with the necessary steps to complete the connection.

. AWith either type of register sender, the regisknown as a marker in which, over contacts not shown on the digit registers, the necessary digits registration is transferred therein. In response to this registration, the marker then operates over certain control circuits to cause the selected trunk to become connected with another trunk to the terminating office or to the called line, whereupon the marker then disconnects and the sender proceeds to complete the connection at the terminating cii'ice or drops ofi if its work has been completed. Since there operations form n0 part ofwmy invention, the same being well-known marker operations, they are not described herein.

While I have described my invention in con-Y nection with its specific application to two representative types of register senders for establishing automatic telephone connections, it is to be understood that various other applications and embodiments thereof may be made by those skilled in the art without departing from the spirit of the invention as defined Within the scope of the appended claims.

What-is claimed is:

.l-.vIn analternating current signal receiver, the combination with` means for amplifying received signals, of means responsive to each signal for altering the amplication factor of said rst mentioned means a predetermined interval after the beginning of each received signal -regardless of the instensity of the signal.

,2. In an alternating current signal receiver, the combination with means for amplifying received signals, of means responsive to each signal for raising the amplification factory of said rstmentioned means a predetermined interval after the beginning of each received signal regardless of the intensity of the signal.

3. In an alternating current signal receiver, the [combination with means for amplifying received signals, of means responsive to each signal for raising the amplification factor of said iirstmentioned means a predetermined interval after the b eginning ofeach received signal regardless of the intensity of the signal.

A. In an alternating current signal receiver, the combination with means for amplifying received signals, of means responsive to each signal for altering the amplification factor of said firstmentioned means a predetermined vinterval after the beginning of the received signal regardless Vof the intensity of the signal, and for restoring the combination with a thermionic amplier, ofV` the amplificationfactor to its originalvalue upon the termination of each signal.

5. In an alternating current signal receiver, the combination with means for amplifying received signals, of means responsive to each signal for raising the amplication factor of said firstmentioned means a predetermined interval after the beginning of each received signal regardless of the intensity ofthe signal, and for restoring said amplification factor to its original value upon the termination of each signal.

'6. In an alternating current signal receiver, the combination with a thermionic amplifier, of means responsive to a signal for altering the'potential applied across the cathode-anode electrodes of the tubes of said amplier a predetermined interval after the beginning of the received mined interval after the beginning of the received signal.

8. In an alternating current signa1 receiver,

means responsive to each signal for increasing the potential applied across the cathode-anode electrodes of the tubes of said amplifier a predetermined interval after received signal.

9. In an alternating current signal receiver, the combination with athermionic ampliiier comprising screen-grid tubes and a source of potential for the electrodes of said tubes, of a network responsive to a received signal for simultaneously raising the potential applied across the cathode-anode electrodes and to the screen electrodes of said tubes a predetermined interval after the beginning of the received signal, said network comprising a main circuit in series with` the cathodes of said tubes, a rst branch circuit connected to the screens of said tubes and second branch circuits connected to said main circuit,

said second branch circuit including means responsive to a received signal for disconnecting said secondvbranch circuit from said main circuit.

10. In an alternating current signal receiver,

EDMUND R. TAYLOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Born g July 20, 1943 Number Keith A May 24, 1932 Curtis Jan. 10, 1939 Hecht et al. Mar. 10, 1942 the beginning of each Green Aug. 13, 1929y V- Ritzman June V9, 1942 Prescott May 16, 1939 Moritz, Jr Apr. 13, 1943 Lundstrom Apr. 8, 1941` 

